This shows an XOR constraint between representedOperation and representedClassifier

We have to schools of thought of what this means

1. There must be 1 Operation associated to a Collaboration or there must be 1 Classifier associated to an Collaboration but not both.

2. The Collaboration can be associated by representedOperation or by representedClassifier but not both.

Assume representatedOperation - this allows a 0..1 multiplicity for operation so it is possible to have no Operation.

Assume representatedClassifier - this allows a 0..1 multiplicity for Classifier so it is possible to have no Classifier.

So in fact a collaboration can have either an Operation or a Classifier or none (but not both)

I go with the latter as I think this is further supported by the wording a little further up in the spec - "A Collaboration may be attached to an Operation or a Classifier". Note _may_ rather than _must_. But that's a tricky point of english and difficult to interpret true meaning.

As far as ArgoUML is concerned this sticks us on the point of whether or not to allow a collaboration/sequence diagram to be created without first forcing the user to create and select the classifer/operation that the collaboration is to be attached to.

It seems most other tools allow collaboration diagrams or sequence diagrams to be created without such associations. How do they allow this if interpretation (1) is the true OMG requirement?